U.S. patent number 7,826,840 [Application Number 11/576,588] was granted by the patent office on 2010-11-02 for method of hand-over in the mixed network of asynchronous communication network and synchronous communication network.
This patent grant is currently assigned to SK Telecom Co., Ltd.. Invention is credited to Jong-Tae Ihm, Hyun-Wook Kim, Nam-Gun Kim, Young-Lak Kim.
United States Patent |
7,826,840 |
Kim , et al. |
November 2, 2010 |
Method of hand-over in the mixed network of asynchronous
communication network and synchronous communication network
Abstract
In the present invention, as a mobile communication terminal,
which is using service in the area of an asynchronous mobile
communication system, detects signals from a synchronous mobile
communication system, the mobile communication terminal repeatedly
performs a process of examining whether, in a predetermined time,
signals from the asynchronous mobile communication system have been
detected a designated number of times, and measuring the intensity
of the signals. When the number of times that the intensity of
signals from the asynchronous mobile communication system is
smaller than a designated number of times, or no signals from the
asynchronous mobile communication system are detected, within the
predetermined time, it is determined whether to perform handover of
the mobile communication terminal.
Inventors: |
Kim; Hyun-Wook (Gyeonggi-do,
KR), Kim; Young-Lak (Gyeonggi-do, KR), Kim;
Nam-Gun (Seoul, KR), Ihm; Jong-Tae (Gyeonggi-do,
KR) |
Assignee: |
SK Telecom Co., Ltd. (Seoul,
KR)
|
Family
ID: |
36647687 |
Appl.
No.: |
11/576,588 |
Filed: |
January 5, 2005 |
PCT
Filed: |
January 05, 2005 |
PCT No.: |
PCT/KR2005/000022 |
371(c)(1),(2),(4) Date: |
December 11, 2007 |
PCT
Pub. No.: |
WO2006/073213 |
PCT
Pub. Date: |
July 13, 2006 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20080207205 A1 |
Aug 28, 2008 |
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Current U.S.
Class: |
455/432.1;
370/331; 455/436; 455/435.2; 455/552.1; 370/328 |
Current CPC
Class: |
H04W
36/14 (20130101); H04W 88/06 (20130101) |
Current International
Class: |
H04W
4/00 (20090101); H04W 36/00 (20090101); H04M
1/00 (20060101) |
Field of
Search: |
;455/432.1,435.2,436,552.1,553.1 ;370/331,328 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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11-136727 |
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May 1999 |
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JP |
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2001-186552 |
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Jul 2001 |
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JP |
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2001-186552 |
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Aug 2001 |
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JP |
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2001-224052 |
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Aug 2001 |
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JP |
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00/74275 |
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Dec 2000 |
|
WO |
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01/03464 |
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Jan 2001 |
|
WO |
|
Primary Examiner: Cho; Un C
Attorney, Agent or Firm: Lowe Hauptman Ham & Berner
LLP
Claims
The invention claimed is:
1. A handover method of a Dual Band Dual Mode (DBDM) mobile
communication terminal in a mobile communication network in which
an asynchronous mobile communication system and a synchronous
mobile communication system coexist, comprising the sequential
steps of: the mobile communication terminal in service with the
asynchronous mobile communication system detecting signals from a
synchronous mobile communication system; if signals from a
synchronous mobile communications system are detected, repeatedly
performing a process of: examining whether a predetermined time
T.sub.wait has elapsed, examining whether the signals from the
asynchronous mobile communication system have been detected a
designated number of times N.sub.max, and measuring the intensity
of the signals from the asynchronous mobile communication system;
and handing over the mobile communications terminal from the
asynchronous mobile communication system to the synchronous mobile
communication system when the measured signal intensity from the
asynchronous mobile communications system is lower than a
predetermined threshold value.
2. The handover method as set forth in claim 1, further comprising:
transmitting, in a System Information Block (SIB) defined by the
asynchronous mobile communication system, information about the
waiting time T.sub.wait for the detection of signals from an
asynchronous mobile communication system, the number of times
N.sub.max that detection is performed, and a waiting time
T.sub.period in a case where no signals from the asynchronous
mobile communication system are detected.
3. The handover method as set forth in claim 1, wherein the step of
examining whether signals from the asynchronous mobile
communication system are detected comprises the steps of: examining
whether a designated waiting time T.sub.period has elapsed when no
signals from the asynchronous mobile communication system are
detected; and measuring the intensity of signals from the
asynchronous mobile communication system when the designated time
T.sub.period has lapsed.
4. The handover method as set forth in claim 3, wherein information
about the waiting time T.sub.period is transmitted to the mobile
communication terminal by the asynchronous mobile communication
system through a System Information Block (SIB).
5. The handover method as set forth in claim 1, wherein the step of
reporting the intensity of the signals to the asynchronous mobile
communication system comprises the step of the mobile communication
terminal transmitting information about a pilot channel of the
synchronous mobile communication system to the asynchronous mobile
communication system.
6. The handover method as set forth in claim 5, further comprising:
transmitting a code, representing a radio environment between the
mobile communication terminal and the synchronous mobile
communication system in a specific field of a message, the message
representing the information about a pilot channel of the
synchronous mobile communication system.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is the National Phase application of International
Application No. PCT/KR2005/000022, filed Jan. 5, 2005, which
designates the United States and was published in English. This
application, in its entirety, is incorporated herein by
reference.
TECHNICAL FIELD
The present invention relates generally to a handover method in a
mobile communication network and, more particularly, to a method
capable of increasing the success rate of handover of a mobile
communication terminal in a mobile communication network in which
an asynchronous network and a synchronous network coexist.
BACKGROUND ART
With the development of mobile communication technology and the
evolution of communication networks, various types of mobile
communication systems have been developed. In order to resolve the
problem of global roaming between the mobile communication systems,
International Mobile Telecommunications (IMT)-2000 systems have
been developed. The IMT-2000 systems are divided into a CDMA
2000-based synchronous system and a WCDMA-based asynchronous
system.
Furthermore, in order to support global roaming between mobile
communication systems, Dual Band Dual Mode (DBDM) mobile
communication terminals usable both in a synchronous system and in
an asynchronous system have been developed. Using such a mobile
communication terminal, it is possible to use different types of
services both in the area of an asynchronous system and the area of
a synchronous system.
Currently, an asynchronous mobile communication system is being
constructed in areas in which high demand for service exists and,
therefore, a synchronous mobile communication system is being
evolved into a form in which the service area thereof includes the
service areas of the asynchronous mobile communication system. When
a user moves between the asynchronous mobile communication system
and the synchronous mobile communication system, handover between
the systems is required in order to provide continuous service.
Particularly, when the mobile communication terminal is located on
the border between an asynchronous area and a synchronous area, or
a shadow area in the communication, such as underground, precise
handover for the mobile communication terminal must be
performed.
FIG. 1 is a conceptual diagram illustrating handover in a mobile
communication network in which an asynchronous network and a
synchronous network coexist.
As illustrated, in the case in which a mobile communication
terminal 10 which is using service in an asynchronous area A moves
into the overlap area of the asynchronous area A and a synchronous
area B (through the movement path C of the terminal), there are
problems in that the intensity of signals between the asynchronous
area A and the mobile communication terminal 10 is similar to that
of signals between the synchronous area B and the mobile
communication terminal 10, and variation in electric field strength
is considerable, so that handover is not precisely performed and it
takes a long time to perform the handover.
DISCLOSURE OF THE INVENTION
Accordingly, the present invention has been made keeping in mind
the above problems occurring in the prior art and an object of the
present invention is to provide a handover method capable of
increasing the success rate of handover by performing handover when
the intensity of signals between a mobile communication terminal
and one mobile communication system, which currently provides
service, is measured a designated number of times and it is
subsequently determined that the mobile communication terminal has
moved into the area of another mobile communication system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a conceptual diagram illustrating handover in a mobile
communication network in which an asynchronous network and a
synchronous network coexist;
FIG. 2 is a flowchart illustrating a general handover method;
and
FIG. 3 is a flowchart illustrating a handover method according to
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, as a mobile communication terminal, which
is using service in the area of an asynchronous mobile
communication system, detects signals from a synchronous mobile
communication system, the mobile communication terminal repeatedly
performs a process of examining whether, in a predetermined time,
signals from the asynchronous mobile communication system have been
detected a designated number of times, and measuring the intensity
of the signals. When the number of times that the intensity of the
signals from the asynchronous mobile communication system is
smaller than a designated number of times, or no signals from the
asynchronous mobile communication system are detected, within the
predetermined time, it is determined whether to perform handover of
the mobile communication terminal.
A mobile communication terminal applied to the present invention is
a DBDM mobile communication terminal, and can provide both
asynchronous mobile communication service and synchronous mobile
communication service. The DBDM mobile communication terminal can
wirelessly access each of an asynchronous mobile communication
system, and a synchronous mobile communication system and use voice
and data services. Furthermore, the DBDM mobile communication
terminal is connected between the asynchronous mobile communication
system and the synchronous mobile communication system, and
transmits and processes signal processing states between the two
systems.
In one mobile communication system, handover (or handoff) refers to
the technology of allowing a user to perform communication without
the disconnection of a call when a mobile communication terminal
moves from one cell to another cell.
The present invention provides a handover method for a DBDM mobile
communication terminal in a network in which an asynchronous mobile
communication system and a synchronous mobile communication system
coexist. The following description is given for the case in which a
mobile communication terminal moves from an asynchronous mobile
communication system into a synchronous mobile communication
system, rather than the case in which the mobile communication
terminal moves from the synchronous mobile communication system
into the asynchronous mobile communication system.
A preferred embodiment of the present invention is described below
in detail with reference to the accompanying drawings.
FIG. 2 is a flowchart illustrating a general handover method.
A mobile communication terminal continuously monitors synchronous
channels and common pilot channels not only for the base station of
an area in which the mobile communication terminal is currently
located but also for neighboring base stations, and measures the
intensities of the signals. When the mobile communication terminal,
which is using service in the area of an asynchronous mobile
communication system, moves into the area of a synchronous mobile
communication system, the intensity of signals from the
asynchronous mobile communication system becomes weak. When the
measured intensity of signals from the asynchronous mobile
communication system is lower than a predetermined value at steps
S101 and S102, the mobile communication terminal reports this to
the asynchronous mobile communication system at step S103.
The asynchronous mobile communication system, having received this
report, becomes aware that the mobile communication terminal is
currently located on the border between the area of the
asynchronous mobile communication system and the area of the
synchronous mobile communication system, determines that handover
to the synchronous mobile communication system is required, informs
the mobile communication terminal of information about the base
stations of a neighboring synchronous mobile communication system,
and directs the mobile communication terminal to measure and report
the intensity of signals from the synchronous mobile communication
system.
As a result, the mobile communication terminal measures the
intensity of signals from the synchronous mobile communication
system at step S105, and reports the measured intensity to the
asynchronous mobile communication system at step S106. The
asynchronous mobile communication system requests handover to the
synchronous mobile communication system by informing the
synchronous mobile communication system of the report of the mobile
communication terminal, Thereafter, the handover is performed
according to a predetermined procedure at step S107.
In the handover method, when variation in the electric field
strength of a wireless communication section is considerable, like
the case where the mobile communication terminal is located on the
border between the area of the asynchronous mobile communication
system and the area of the synchronous mobile communication system,
it is impossible to perform precise handover. For example, when the
mobile communication terminal, which has moved from the area of an
asynchronous mobile communication system into the overlap area
between the areas of the asynchronous and synchronous mobile
communication systems, and then moves from the overlap area into
the area of the synchronous mobile communication system, handover
from the asynchronous mobile communication system to the
synchronous mobile communication system is performed.
However, when the mobile communication terminal immediately moves
back to the overlap area, and the intensity of signals from the
asynchronous mobile communication system is greater than that of
signals from the synchronous mobile communication system in the
overlap area where the mobile communication terminal is ultimately
located, the quality of a call decreases or the call is
disconnected, so that handover must be performed again.
Therefore, handover must be performed when the intensity of signals
from a different mobile communication system is stable upon
movement of a mobile communication terminal.
For this purpose, in the present invention, as a mobile
communication terminal, which is using services in an asynchronous
mobile communication system, detects signals from a synchronous
mobile communication system, it repeatedly performs a process of
examining whether, in a predetermined time, signals from the
asynchronous mobile communication system have been detected a
designated number of times, and measuring the intensity of the
signals. Handover is performed when the measured signal intensity
is lower than a predetermined threshold value.
FIG. 3 is a flowchart illustrating a handover method according to
the present invention.
A mobile communication terminal, which is using service in an
asynchronous mobile communication system, continuously monitors the
synchronous channels and common pilot channels not only for the
base station of an area in which the mobile communication terminal
is currently located, but also for neighboring base stations at
step S201.
In this case, when signals from the synchronous mobile
communication system are detected at step S202, the mobile
communication terminal waits for a predetermined Time. T.sub.wait,
at step S203. The number of times that the intensity of signals
detected from the asynchronous mobile communication system has
reached a designated number of times, N.sub.max, is then examined
at step S204. If, as a result of the examination, the number of
times that the intensity of signals from the asynchronous mobile
communication system is determined to be below the designated
number of times N.sub.max, whether or not signals from the
asynchronous mobile communication system are detected is examined
at step S205. The intensity of the signals is measured when the
signals are detected at step S208. Steps S203, S204 and S205 are
repeatedly performed a designated number of times N.sub.max, while
the number of times that signals from the asynchronous mobile
communication system are detected is increased.
After examining whether a predetermined time T.sub.wait has elapsed
and examining whether signals from the asynchronous mobile
communication system have been detected a designated number of
times N.sub.max, it is determined whether the intensity of the last
signals from the asynchronous mobile communication system is larger
than a predetermined threshold value at step S207. If the intensity
is larger than the predetermined threshold value, the process
returns to step S201 of monitoring the asynchronous mobile
communication system and the synchronous mobile communication
system.
Meanwhile, when no signals from the asynchronous mobile
communication system are detected at step S205, in which whether or
not signals from an asynchronous mobile communication system are
detected is examined, a designated time, T.sub.period, elapses at
step S209 and the process then proceeds to step S206 of measuring
the intensity of signals from the asynchronous mobile communication
system.
In this case, it is preferable that information about a waiting
time T.sub.wait for the detection of signals from an asynchronous
mobile communication system, the number of times N.sub.max that
detection is performed, and a waiting time T.sub.period in the case
where no signals from an asynchronous mobile communication system
are detected are transmitted using the System Information Block
(SIB) of the asynchronous mobile communication system. The waiting
time T.sub.wait may be set to, for example, 30 to 90 seconds, the
number of times N.sub.max that detection is performed may be set
to, for example, 8 to 12, and the waiting time T.sub.period in the
case where no signals from the asynchronous mobile communication
system are detected may be set to, for example, 4 to 6 minutes.
Furthermore, when the measured intensity of signals from the
asynchronous mobile communication system is below the predetermined
threshold value at step S207, the mobile communication terminal
reports this to the asynchronous mobile communication system at
step S208.
The asynchronous mobile communication system determines that the
mobile communication terminal requires handover to the synchronous
mobile communication system based on the report from the mobile
communication terminal, and causes a handover procedure to be
performed between the asynchronous mobile communication system, the
mobile communication terminal, and the synchronous mobile
communication system.
For the performance of the handover, the mobile communication
terminal transmits information about the pilot channel of the
synchronous mobile communication system to the asynchronous mobile
communication system, thereby allowing the asynchronous mobile
communication system to easily direct the handover. Particularly,
in the present invention, when transmitting information about the
pilot channel of the synchronous mobile communication system to the
asynchronous mobile communication system, the mobile communication
terminal assigns a specific value (for example, `0`) to a
scrambling code which is a field defined by the asynchronous mobile
communication system, so that there are advantages in that the base
station of the asynchronous mobile communication system can easily
become aware of the radio environment of the synchronous mobile
communication system, and a search for the base station of the
synchronous mobile communication system can be performed using
signals from the asynchronous mobile communication system.
Since a detailed handover procedure is performed according to a
procedure designated by the operator of a mobile communication
system, a detailed description thereof is omitted. It is preferable
to employ a method capable of more rapidly performing a handover
without the occurrence of call disconnection during the
handover.
Those skilled in the art can understand that the present invention
can be implemented in specific forms without alteration of the
technical spirit and essential characteristics of the invention. As
a result, it is to be understood that the above-described
embodiment is illustrative in all respects, and not restrictive.
The scope of the present invention is defined by the accompanying
claims rather than the detailed description, and modifications and
variations, which are derived from the spirit and scope of the
claims and equivalents thereto, are included in the scope of the
present invention.
INDUSTRIAL APPLICABILITY
According to the above-described present invention, in a mobile
communication network in which an asynchronous mobile communication
system and a synchronous mobile communication system coexist, the
mobile communication terminal detects signals from the synchronous
mobile communication system, examines whether signals from the
asynchronous mobile communication system have been detected a
designated number of times, and allows handover to be performed
when the intensity of signals from the asynchronous mobile
communication system is lower than a predetermined threshold value,
so there is an advantage in that the handover is precisely
performed.
* * * * *